According to U.S. Pat. 2,962,372, tantalum and niobium are extracted and separated by digestion of corresponding raw materials with hydrofluoric acid and acidification with sulfuric acid or hydrofluoric acid, Along with certain accompanying elements, the tantalum and niobium components dissolve to form complex heptafluorides H.sub.2 TaF.sub.7 and H.sub.2 NbF.sub.7 or H.sub.2 NbOF.sub.5. After filtration from insoluble residue (alkaline earth fluorides, rare earth fluorides), the aqueous hydrofluoric or hydrofluoric-sulfuric acid solution containing tantalum and niobium is contacted with an organic extractant, such as for example methyl isobutyl ketone (MIBK), in a multistage mixer-settler plant.
The complex niobium and tantalum dissolve in the organic ketone phase and are extracted together while most of the impurities and accompanying elements, such as iron, manganese, titanium, etc. remain in the extraction raffinate. In practice a raw materials digestion solution throughout and extraction conditions are used so that concentrations of 150 to 200 g/l Nb.sub.2 O.sub.5 +Ta.sub.2 O.sub.5 are obtained in the organic phase. The niobium is re-extracted from the organic phase with water or dilute sulfuric acid. The aqueous phase takes up the complex niobium fluorides dissolved in the ketone, sulfuric acid and free hydrofluoric acid whereas the tantalum-fluoro compounds remain dissolved in the organic phase.
To remove traces of tantalum re-extracted with the niobium, the aqueous niobium solution is re-contacted with a small quantity of MIBK. This organic phase resulting is returned to the tantalum/niobium coextraction stage. The niobium oxide hydrate (niobium hydroxide) is precipitated by addition of gaseous ammonium or ammonia dissolved in water. After reextraction of the tantalum from the organic phase with water or dilute ammonia solution, tantalum may be precipitated as oxide hydrate with ammonia or, by addition of potassium salts, as K.sub.2 TaF.sub.7, K.sub.2 TaF.sub.7 is a starting material for the production of tantalum metal.
Considerable volume streams of heavily polluted waste-waters accumulate in (he described process, including metal-salt-containing hydrofluoric acid/sulfuric acid solutions from the raffinate and the washing acid and highly dilute NH.sub.4 F and/or NH.sub.4 F/NH.sub.4).sub.2 SO.sub.4 solutions from the precipitation processes. These waste waters have to be worked up, large quantities of gypsum/fluorspar sludges being formed in the process; these sludges have to be disposed of. Approximately 9 to 10 tons of sludge for disposal accumulate per ton of raw material/starting material.
In addition, the current purity requirements of &gt;99.9% cannot be met by this process.
Accordingly, the object of the present invention is to provide a process which would not have the abovementioned disadvantages of the prior art.